Feel if the plug gets warm where frig plugs into the wall. Any dirty connection can cause this. I agree with Henry as well, could be something loose or dirty there as well.
Add up what else is on the line with the frig. Frig draws about 1500 watts at startup, then about 900 when running. Add to that some lights (400 watts?) and some receptacles (microwave 800 watts? TV 600 watts? Sweeper 600 watts?) Make sure that you are not overloading the circuit. 20 amp at 117 volts handles a little over 2000 watts.